Endoscopy is a minimally invasive procedure for the real-time acquisition of video images of the interior surfaces of an organ with a flexible or rigid endoscope. Endoscopy is often used to allow a biopsy to be taken. Significant problems for many endoscopies are biopsy site detection, path planning to reach the site, and re-localisation (re-identification) of the site during the same or a future examination. For example, many endoscopic procedures (such as oesophageal endoscopy for Barrett's Oesophagus) require the endoscopist to return to a location previously identified to take a measurement or extract a small sample of tissue (biopsy) for analysis of cellular structure and/or to detect the presence of pathology, in particular cancer and pre-cancerous conditions. Re-localisation may be required during the procedure as the endoscope may move, the patient may cough etc, or it may be required at a later date in order to assess disease progression.
One particular method is known as optical biopsy. This method is based on the properties of light to make a diagnosis in vivo and in situ during endoscopy, while the diagnosis is traditionally done by histological or cytological analysis. It has been shown that optical biopsies contribute to a better detection of malignancy which is invisible during endoscopy and improve the accuracy of the diagnosis. However, it is difficult in practice to have a good match between a tissue sample extracted for histology and the extent scanned during optical biopsy. As a result, many extracted samples may present irrelevant information, which brings great difficulties to the clinicians to diagnose, screen, stage and treat diseases.
In bronchoscopy, for example, an attempt has been made to solve these problems with a guidance system based on tracking the bronchoscope during the examination in relation to a pre-operative CT image (see Helferty J. P. et al., “Computer-based system for the virtual-endoscopic guidance of bronchoscopy”, October-November 2007, Computer Vision and Image Understanding, Vol. 108, Issues 1-2, pp. 171-187; and Mori K. et al., “Bronchoscope tracking without fiducial markers using ultra-tiny electromagnetic tracking system and its evaluation in different environments”, October 2007, Medical Image Computing and Computer-Assisted Intervention (MICCAI'07), Vol. 4792 of Lecture Notes in Computer Science, pp. 664-651, Springer-Verlag). Such systems have helped to localise biopsy sites with a precision of 1.58 mm (Helferty J. P. et al.). Nevertheless, some examinations like gastroscopy are based only on video images. Therefore, the endoscopist may want to use miniprobes that are inserted into the working channel of the endoscope and that return additional microscopic information (in vivo histology) or any other signal from the tissue in order to detect and localise biopsy sites. When the endoscopist detects a suspicious region, it is scanned with the miniprobe in contact with the tissue surface in order to confirm the diagnosis. If a tissue sample needs to be extracted from this region, the miniprobe is replaced with forceps.
A significant problem for applications in endoscopy procedures based on video images only and for gastroscopy in particular is that biopsies are performed by interactive guidance of the forceps by the endoscopist. Therefore, once a biopsy site has been detected with a miniprobe, for example, at the tissue surface, it needs to be re-localised precisely in the next video images in order to go back to the same position with the forceps. The problem of object localisation in video images has recently been addressed in applications for minimally invasive surgery (see Speidel S. et al., “Tracking of Instruments in Minimally Invasive Surgery for Surgical Skill Analysis”, MIAR 2006, Vol. 4091 of Lecture Notes in Computer Science, pp. 148-155, Springer-Verlag; and Voros S. et al. “Automatic Localization of Laparoscopic Instruments for the Visual Servoing of an Endoscopic Camera Holder”, 2006, Medical Image Computing and Computer-Assisted Intervention (MICCAI'06), Vol. 4190 of Lecture Notes in Computer Science, pp. 535-542, Springer-Verlag). However, these documents focus only on tracking the instrument tip and its trajectory for robotized-assisted surgeries.
The above problems are also relevant to other medical applications where a point site needs to be re-localised, for example for accurate therapy delivery. In addition, similar problems also apply to non-medical applications such as industrial inspection; remote sensing in hostile environments or very remote sites, for example, underground or underwater, or in space exploration; remote manipulation and repair; and telerobotics.